The conventional process for the production of N-alkyl aniline involves the batch scale reduction of nitrobenzene to produce aniline which is then alkylated to produce the corresponding N-alkyl aniline. Typical of the alkylation-reduction processes are those found in U.S. Pat. No. 2,580,284; J. Am. Chem. Soc. 1955,77,4052; J. Am. Chem. Soc. 1956,78,1635; and J. Org. Chem. 1956,21,474. Kinetics and Catalysis, 1982,23(1), 56 reports a 56% yield of secondary amine and a 32% yield of the tertiary amine with a 160 minute reaction time in a batch process for the reaction of nitrobenzene and n-propanal at 45.degree. C. increasing to 98% secondary amine and 0% tertiary amine in 465 minutes at 20.degree. C. Several patents report the exclusive preparation of tertiary amines from the reaction of aldehydes with aniline and hydrogen utilizing a Pt/C catalyst. (see Chem. Abstr. 155 7362m, 71108v, 28878j; 110 59530r; and 109 149060w) The reduction of nitrobenzene to produce aniline involves hydrogenating the nitrobenzene in the presence of catalysts such as platinum, palladium, nickel, noble metal catalysts, or oxides of platinum, palladium, or noble metal catalysts. Gaseous hydrogen is commonly used as a reducing agent. The alkylating agent is usually an aldehyde or alcohol. If the alkylation is carried out with an alkyl alcohol, the product is usually a mixture of the secondary and tertiary amine. If the reaction is carried out with an aldehyde, the intermediate imine is hydrogenated to form, predominately the secondary amine. The reaction medium can be any non-interfering solvent. Preferred solvents include water, alcohols, and water-alcohol mixtures, or other inert medium.
Unfortunately, it has been found that nitro reductions, especially of aromatic compounds involve the sequential reduction of highly reactive and unstable intermediates, including nitroso-, hydrazo-, azo-, and azoxy-compounds. These reactive intermediates can lead to several undesirable by-products, which are often very highly colored. The batch reductions cannot minimize these reactive intermediates. In the batch process, the heat release from the reaction continually changes rendering it difficult to provide accurate temperature control.
It has been known to reduce aromatic nitro compounds on a continuous basis in a stirred tank reactor. However, the use of a stirred tank reactor to conduct a one-step process in which an aniline and the alkylated derivative thereof are formed concurrently on a continuous basis has not been previously suggested in the prior art.